1. Field of the Invention
The present invention relates to a sensor for cylinder control which is capable of detecting the operational state of a piston of a cylinder, for example of detecting that the piston has reached the end of its stroke, and to a cylinder device which incorporates such a sensor.
2. Description of the Related Art
Generally a large number of hydraulic cylinders are employed in machines which manufacture automobile parts and the like by metal or plastic casting using metal molding. Recently, in response to greater demands for accurate control of the forward and reverse stroke of such reciprocating cylinders used in production machinery for casting or the like, the machine operation has become more and more automated by the provision of sequence circuitry.
For example, as a prior art technique for cylinder control, as shown in FIG. 12, there is a control technique in which, by a limit switch device 2 which employs an analog switch or a contact switch or the like and which is fitted to a cylinder main device 1, the position in the forward and reverse direction is detected, and a signal is despatched to a control board to stop the cylinder via a changeover valve (a solenoid valve). Furthermore, there is a control technique in which a sensor is housed within the cylinder and detects its position in the forward and reverse direction, and alters the stroke adjustment by a pulse signal, converts it into data by a detection device and again despatches the signal to the control board, and stops the cylinder via a changeover valve. Yet further, in Japanese Patent Publication Heisei 7-42965, there is proposed a technique of providing a sub-cylinder which is synchronized with said main cylinder, and of detecting and controlling the position in the forward and reverse direction by adjusting the amount of hydraulic fluid which flows into said sub-cylinder.
However, with these prior arts of cylinder control, the following problems still remain. In detail, in the case of a prior art limit switch device, the limit switch can easily suffer damage due to high temperature, large quantities of mold release agent or sludge, and it may happen that trouble with metal molds caused by this type of problem can be a great obstruction to production. Furthermore, since the tip portion is installed in the workplace, electrical leakage can easily happen even if waterproof type switches are employed because water, oil, and flash regularly impact thereon, and also there is the danger that the cables to the limit switch device may be cut. Yet further, along with the fact that it may be the case that no space is available to fit the limit switch device within the cylinder main body, also high precision adjustment of the limit switch device according to the size of the cylinder (according to its stroke) may be required. Moreover, if a plurality of cylinders are present, it is necessary to fit an individual limit switch device for each cylinder, and, along with inviting increase in the number of parts and high cost, there is the inconvenience that, if all of the cylinders are controlled using one circuit, this control becomes difficult because it becomes more complicated.
Also, if the sensors are housed internally, since pulse signals are employed, along with the requirements to adjust the drive section inside the cylinder in accordance with the cylinder stroke and to connect it to detectors, there is also a danger of erroneous operation being caused due to the magnetic field which is generated being weak.
Yet further, if control is performed according to the amount of hydraulic fluid which flows into a sub-cylinder, along with the necessity for a blocking member in the main cylinder, it is also necessary to adjust the amount of fluid which flows in. Accordingly there has been felt the desirability of providing a technique which utilizes a more simple structure and which also makes it unnecessary to adjust the amount of hydraulic fluid.
The present invention has been conceived in consideration of the above described problems, and its objective is to provide a sensor for cylinder control and a cylinder device incorporating the same, which avoid the occurrence of erroneous operation due to the possibility of connections coming off from the cylinder, and which can make it unnecessary to perform adjustments according to the size of the cylinder, or to adjust the quantity of fluid.
The present invention uses the following structure for solving the above described problems. Namely, the sensor for cylinder control of the present invention is connected to a main cylinder having an internal cylinder chamber which is partitioned by a piston into two chambers, and which detects the operational state of said piston, and is characterized by comprising: an accumulator which is connected via a connecting conduit to one of said two chambers and whose interior is pressurized by fluid expelled from said one chamber; and a stop signal generation mechanism which generates a signal which stops the driving of said main cylinder due to pressure differential between said accumulator and said connecting conduit which is generated at the instant that the increase of pressure from said one chamber stops.
With this sensor for cylinder control, since the accumulator is incorporated which is connected via the connecting conduit to one of said two chambers so that its interior is pressurized by hydraulic fluid expelled from said one chamber, thereby the hydraulic fluid which is expelled from the chamber (said one chamber) of the main cylinder by the shifting of the piston flows into the accumulator via the connecting conduit, so that the pressure in the accumulator rises. And immediately before the piston, for example, arrives at the end of its stroke, a high surge pressure is generated, so that the pressure in the accumulator rises. Furthermore, at the instant that the piston arrives at the end of its stroke, the pressure of the hydraulic fluid in the chamber abruptly drops, so that the pressure supplied to the accumulator from the connection conduit abruptly drops. At this time, a pressure differential is caused between the accumulator which is in a high pressure state and the connecting conduit in which the pressure has abruptly dropped.
With the present invention, since there is provided a stop signal generation mechanism which generates a signal for stopping the driving of the main cylinder due to pressure differential between the accumulator and the connecting conduit which is generated at the instant that the increase of pressure from said one chamber stops, therefore the stop signal is generated due to the pressure difference which is generated at the instant that the piston arrives at the end of its stroke, and it is possible to stop the driving of the main cylinder. Accordingly, with the present invention, it is possible to stop the main cylinder reliably and also at high speed, directly before the piston arrives at the end of its stroke.
Furthermore, according to another aspect of the present invention, in this sensor for cylinder control, the technique may be employed of making the stop signal generation mechanism comprise a non-return valve provided in the connecting conduit which suppresses flow of fluid towards the one chamber, a first branch conduit of which a one end is connected to the connecting conduit between the accumulator and the non-return valve, a second branch conduit of which a one end is connected to the connecting conduit between the one chamber and the non-return valve, and a switch mechanism which is connected to the other end of the first branch conduit and to the other end of the second branch conduit and which generates the signal when the pressure in the first branch conduit becomes higher than the pressure in the second branch conduit.
With this sensor for cylinder control, due to the pressure differential which is generated at the instant when for example the piston reaches the end of its stroke, although an attempt is made to expel the hydraulic fluid from the accumulator towards the connecting conduit and the first branch conduit, because the non-return valve is present, therefore the fluid only flows to the side of the first branch conduit. Furthermore, the pressure in the first branch conduit becomes greater than the pressure in the second branch conduit, because the pressure in the second branch conduit as well which is connected to the connecting conduit from said one chamber in which the pressure has at the same time abruptly dropped as far as the non-return valve is low. Accordingly, at this time, a signal is generated by the switch mechanism to stop the driving of the main cylinder. In this manner, with the present invention, since a pressure differential is generated between the pressure in the first branch conduit and the pressure in the second branch conduit due to the non-return valve which is provided in the connecting conduit, accordingly it becomes easy for the stop signal to be generated.
Furthermore, according to another aspect of the present invention, in this sensor for cylinder control, it is desirable for the switch mechanism to further include a sensor cylinder which comprises a cylinder chamber which is partitioned by a piston into two chambers, and a switch section which generates the signal mechanically by the shifting of the piston of the sensor cylinder or electrically by a pressure sensor; and one of the chambers of the sensor cylinder is connected with the interior of the first branch conduit, while the other of the chambers of the sensor cylinder is connected with the interior of the second branch conduit.
Since with this sensor for cylinder control, along with connecting the one chamber of the sensor cylinder with the interior of the first branch conduit, also the other of the chambers of the sensor cylinder is connected with the interior of the second branch conduit, therefore, when the pressure in the first branch conduit becomes higher than the pressure in the second branch conduit, it is possible to generate the stop signal by the switch section operating mechanically by the shifting of the piston of the sensor cylinder or electrically by a pressure sensor, and accordingly it is possible to provide reliable operation with a simple and moreover cheap structure.
Furthermore, according to another aspect of the present invention, in this sensor for cylinder control, the technique may be employed of making the stop signal generation mechanism comprise: a non-return valve provided in the connecting conduit which suppresses flow of fluid towards the one chamber; a first branch conduit whose one end is connected to the connecting conduit between the accumulator and the non-return valve; a sensor cylinder which is connected to the other end of the first branch conduit and which comprises a piston which can be shifted by fluid which flows in from the first branch conduit; a switch section which generates the signal mechanically by shifting of the piston of the sensor cylinder or electrically by a pressure sensor; and a shift suppression mechanism which suppresses shifting of the piston of the sensor cylinder against opposition of pressure in the first branch conduit which is lower than the pressure when the pressure differential is generated.
With this sensor for cylinder control, since there is provided the shift suppression mechanism which suppresses shifting of the piston of the sensor cylinder opposing the pressure in the first branch conduit which is lower than the pressure when the pressure differential is generated, accordingly since, while the piston of the main cylinder is shifting, the pressure in the first branch conduit is a lower pressure than the pressure when generating the above described pressure differential, therefore due to the shift suppression mechanism the piston of the sensor cylinder does not shift. And since, when the piston of the main cylinder reaches the end of its stroke, along with the above described pressure differential being generated, also flow of hydraulic fluid into the connecting conduit on the upstream side is suppressed by the non-return valve, accordingly the pressure in the first branch conduit abruptly increases and exceeds the pressure which can be suppressed by the shift suppression mechanism, and the piston of the sensor cylinder shifts and the above described signal is generated by the switch section.
Furthermore, according to another aspect of the present invention, in this sensor for cylinder control, it is desirable for the accumulator to be a synchronizing cylinder comprising a piston which can be shifted by fluid which flows in from the connecting conduit, and to include a load mechanism which applies load to the piston of the synchronizing cylinder to shift it, when fluid flows in from the connecting conduit.
With this sensor for cylinder control, since there is included the load mechanism which applies load to the piston of the synchronizing cylinder to shift it, when fluid flows in from the connecting conduit, therefore, although the piston of the synchronizing cylinder shifts when hydraulic fluid flows into the synchronizing cylinder from the connecting conduit, at this time, load is imposed by the load mechanism, and, along with increasing the pressure within the synchronizing cylinder, the internal volume of the chamber increases. Furthermore, at the instant that the piston of the main cylinder reaches the end of its stroke, when the pressure in the connecting conduit abruptly drops, a pressure differential is generated between the synchronizing cylinder and the connecting conduit, so that hydraulic fluid flows from the synchronizing cylinder to the side of the connecting conduit, and the stop signal for main cylinder driving is generated. In other words, it is possible to ensure a sufficient pressure differential and fluid amount for generating the stop signal.
Furthermore, according to another aspect of the present invention, in this sensor for cylinder control, it is desirable for the accumulator to be a large diameter conduit whose internal diameter is set to be larger than that of the connecting conduit.
With this sensor for cylinder control, since the accumulator is a large diameter conduit whose internal diameter is set to be larger than that of the connecting conduit, therefore the pressure in the interior of the large diameter conduit is increased by the inflow of hydraulic fluid from the connecting conduit, and it is possible to accumulate a great deal of pressure energy therein due to its large internal diameter, so that it is possible to provide the beneficial effect of an accumulator with an extremely simple structure.
Furthermore, according to another aspect of the present invention, in this sensor for cylinder control, it is desirable for the stop signal generation mechanism to comprise an erroneous operation detection mechanism which sets in advance as a normal operating time period the time period until the piston of the main cylinder arrives at the end of its stroke during normal operation and the stop signal is generated, and generates a signal indicative of erroneous operation, when the stop signal for the driving of the main cylinder is generated in a time period which is shorter than the normal operating time period.
With this sensor for cylinder control, since there is included the erroneous operation detection mechanism which generates a signal indicative of erroneous operation, when the stop signal for the driving of the main cylinder is generated in a time period which is shorter than the normal operating time period, therefore if for example in metal mold forming or the like the piston stops at an intermediate point of its travel due to flash or the like, although a pressure differential identical to that during normal operation is generated and the stop signal is generated, in this case it is possible for the erroneous operation detection mechanism to detect that erroneous operation has occurred, since the stop signal has been generated more quickly than the normal operating time period.
Moreover, according to a different aspect of the present invention, a cylinder device according to the present invention comprises a main cylinder comprising an internal cylinder chamber which is partitioned by a piston into two chambers, and is characterized by comprising to a sensor for cylinder control of any of the above described types according to the present invention, which is connected at least one of said two chambers.
With this cylinder device, since a sensor for cylinder control of any of the above described types according to the present invention is provided and is connected at least one of said two chambers, thereby it is possible to stop the driving of the main cylinder reliably and at high speed, since this sensor for cylinder control generates a stop signal at the instant that the piston of the main cylinder arrives at the end of its stroke.
Furthermore, according to another aspect of the present invention, in this cylinder device, it is desirable for there to be further included a pair of supply and drain conduits of which the one ends are connected to the two chambers of the main cylinder and which supply and drain fluid thereto and therefrom, and a changeover valve which is connected to the other ends of the pair of supply and drain conduits, and for the sensor for cylinder control to be provided so as to connect the connecting conduit to at least one of the pair of supply and drain conduits.
With this cylinder device, since the sensor for cylinder control is provided as connecting the connecting conduit to at least one of the pair of supply and drain conduits, thereby it is possible to operate the sensor for cylinder control with the hydraulic fluid which flows into the connecting conduit via the pair of supply and drain conduits which supply and drain fluid to and from the main cylinder to drive it, and it is possible to manage without connecting the connecting conduit directly to the main cylinder, so that it is possible to construct the pipework in a simple manner.
Furthermore, according to another aspect of the present invention, in this cylinder device, it is desirable to provide a plurality of the main cylinders, and to connect the sensor for cylinder control so that the connecting conduit branches to the plurality of main cylinders.
With this cylinder device, since the connecting conduit of the sensor for cylinder control is connected to the plurality of main cylinders by being branched, thereby it is possible, for example, to control a plurality of main cylinders which have different outputs by a single sensor for cylinder control.
Furthermore, according to another aspect of the present invention, in this cylinder device, it is desirable for the sensor for cylinder control to be disposed at the changeover valve. In other words, since with this cylinder device the cylinder control sensor is located at the changeover valve, it is possible to anticipate combination and unification with the changeover valve, and thereby it is possible to make the entire system more compact and to reduce its cost.